LLMs now slot in first or second, typically completely eliminating SO. Others still provide value.

The easiest and quickest is to throw up your hands, give up and do something else. I suspect your question doesn't expect that option, but it usually is an option.

Why not AI? If what you are working with has been around for a while and is widely used, then with a bit of careful context setting AI beats searching by other means. AI is only as useful as the information that was scrapped from numerous sources correlates to your context and question.

You could raise a support ticket with the product and hope that somebody can solve your problem.. In my experience this can be rather fruitful or futile yelling into the void.

Then you could attempt to solve your problem by going about it in a different way. This requires backing up and trying different directions. It is always possible that the way you are trying to solve a problem is an edge case that the original designers / implementers didn't anticipate.

If you are really determined, then you have the option of digging into the code, determining how it works, etc. This can be a very deep dive into a rabbit hole. At the bottom of the rabbit hole you will have studied and understood stuff you didn't even know existed and grappling with disassembled machine code. Going this deep is rare but not unheard of.